Trump to Clinton: 'No more Mr. Nice Guy'

US Republican presidential nominee Donald Trump says he's taking the gloves off in his battle against Democrat Hillary Clinton in the race for the White House, after taking a scorching from speakers at the Democratic National Convention.

Trump wrapped up a five-day, seven-state campaign swing in Colorado on Friday, where for a fifth straight day his supporters chanted "lock her up" whenever he brought up Clinton's name.

Trump supporters say Clinton deserves to be prosecuted for her handling of US foreign policy as President Barack Obama's first-term secretary of state and for her use of a private email server while in that office.

All week Trump has sought to tamp down the chants by stressing that his main goal is to simply beat Clinton in the November 8 presidential election.

Donald Trump. (AP) ()

But as the crowd chanted the slogan in Colorado Springs, Trump finally relented.

Trump was a punching bag at the Democratic convention in Philadelphia, which wrapped up on Thursday night, as speaker after speaker - including some Republicans - said he lacked the temperament to be president. Clinton herself said in her acceptance speech that the election represented a "moment of reckoning" for the country.

Later in his stump speech, Trump criticised Clinton sharply, but got sidetracked by a couple of disputes from last year as he tried to rebut a Clinton campaign ad.

That ad uses video clip from Trump's attack on Fox News anchor Megyn Kelly in protest of her questioning of him at a debate of Republican presidential contenders last August when he said afterward that blood was "coming out of her eyes, coming out of her wherever."

"I was talking about her nose," Trump said in Colorado Springs.

"I wanted to get back on the issue of taxes" at the debate.

Trump also brought up the case of disabled New York Times reporter Serge Kovaleski, whom Trump seemed to mock publicly in video used by the Clinton ad.

Trump said he was depicting the reporter grovelling to him.

"I didn't know he was disabled. I didn't know it at all. I had no idea," he said.